Turbochargers are used in conjunction with internal combustion engines in vehicles (e.g., trucks, automobiles, tractors, etc.) to increase power output, improve efficiency, lower emissions or to achieve a combination of these advantages or improvements. A turbocharger is comprised of a turbine that converts kinetic energy in the combustion products exhausted from the engine into mechanical work that is transmitted to a compressor that draws in ambient air and discharges the air at a higher pressure. The higher pressure air discharged from the turbocharger compressor is conveyed to the air intake manifold of the internal combustion engine, providing a higher mass flow of oxygen to the cylinders. The increased mass flow of oxygen is accompanied by an increased mass flow of fuel to the cylinders leading to more combustion and power per piston stroke.
Shown in FIGS. 1 and 2 is a conventional compressor wheel 100. Compressor wheel 100 has a base portion 112, a hub portion 114 that projects generally perpendicularly from the base portion 112. The upper surface 116 of base portion 112 gradually curves upwardly from wheel edge 118 toward hub portion 114. Projecting radially outwardly from hub portion 114 and upwardly from base portion 112 are a plurality of primary blades 120. Primary blades 120 are spaced apart by equal angles around the hub portion 112. In the illustrated compressor wheel 100, there are six primary blades 120 separated by 60 degree angles. Disposed between each pair of adjacent primary blades 120 is a shorter secondary blade 122. Each of the primary and secondary blades 120, 122 have an upper inducer edge 124 and 126, respectively, a vertical inducer edge 128 and 130, respectively, an upper exducer edge 132 and 134, respectively, and a vertical exducer edge 136 and 138, respectively. The vertical inducer edges 128 and 130 define the radial outer boundary of the inducer section and inducer diameter 140 of the compressor wheel 100, and the vertical exducer edges 136 and 138 define the radial outer boundary of the exducer section and exducer diameter 142 of the compressor wheel 100. Generally, the inducer portion of the compressor wheel 100 and blades 120, 122 draw air axially inwardly into the compressor volume defined by a compressor housing, and the exducer portion of the compressor wheel 100 and blades 120, 122 cause compressed air to exit the compressor radially. The shorter or secondary blades 122, also known as splitter blades, are believed to allow higher intake air mass flow through the inducer at very high rotational speeds. While secondary blades 122 can be desirable for certain applications, compressor wheels having all blades being identical are also very common and useful.
Conventional compressor wheels 100 for turbochargers have a threaded through bore 144 that is threadingly engaged with external threads of a shaft coupled to a turbine wheel configured to be driven by exhaust gases from an internal combustion engine. The upper end of hub portion 114 is provided with an integral hexagonal nut 146 that allows compressor wheel 100 to be tightly secured to the shaft, such as with a wrench.